Left exposed to the elements, different materials break down at very different rates – ranging from a matter of days to many thousands of years. But how long does it take some of the most everyday materials to break down?
We’re going to take a look at the decomposition times of some common materials, how this looks in the real world, and whether there might be a better solution than just leaving things to rot.
To begin, let’s clarify how decomposition actually works and the factors that affect it.
How Do Biodegradable Materials Decompose?
To start with, decomposition is the breakdown of matter by organisms such as bacteria and fungi. The main factors that affect decomposition are temperature, water, and oxygen.
A warmer environment promotes the reproduction of microorganisms and faster decomposition of materials – up until it becomes too hot for them to survive. A cold environment will hinder, or entirely stop, the decomposition process.
In addition to a warm environment, the organisms that decompose materials also require water to survive, meaning a wetter environment will generally encourage a faster breakdown. However, just like with temperature, there is a delicate balance – too wet an environment and the water will drive the air from a material, stopping the decay organisms from being able to survive.
That takes us to the final factor – oxygen. Since it is organisms that are responsible for breaking down materials that decompose, they require oxygen in order to respire. This factor is often in short supply at landfills, which is one of the reasons it can take significantly longer for materials to break down in landfills than if they were on the surface.
It is important to remember that there are materials that don’t decompose. When we talk about some materials “decaying,” such as glass, plastic and metal, we are really talking about them breaking down. These breakdowns don’t rely on decomposers like bacteria and fungi – they generally don’t eat inorganic material – but rather factors such as photodegradation, oxidation, and abrasion.
There are, of course, exceptions to this, with an increasing amount of research being done on areas such as using bacteria or enzymes to break down plastics.
How Is Decomposition Time Measured?
When discussing what materials take the longest to decompose, it is common to hear that some items will take hundreds or thousands of years to break down. However, this isn’t based on historical records – we haven’t had these materials long enough. So how exactly is biodegradability measured?
The most common method of estimating how long different materials take to decompose is through the use of respirometry tests. In these tests, waste is placed in a container with the organisms and conditions necessary for decay. Over a period of days, microorganisms start digesting the waste and respiring. This respiration produces carbon dioxide, which is measured and used as an indicator of the rate of decay.
Relying on decay proper, this test is not appropriate for materials that don’t decompose such as plastics and glass – microorganisms can’t digest these materials. Therefore, to estimate the timeframe for these substances, scientists rely on observation of other forms of degradation – for example, how rapidly ultraviolet radiation breaks the polymers of a plastic (photodegradation). This isn’t overly accurate, which is why there are such varying estimates for how long some modern materials will actually take to break down. However, most scientists agree that whether it is 500 years or 4000 years, it is a very long time.
How Long Does It Take for Different Materials to Decompose or Break Down
For an overview of how quickly some of the most common materials decompose or break down, take a look at the table below.
It’s worth noting that these times will vary dramatically depending on conditions.
What’s more, many everyday items are made up of more than one material, meaning that a single household object will likely decay at different rates. So, what might the breakdown of a common piece of trash look like?
How Objects Break Down – A Discarded Armchair
Driving through a city, it’s common to see old armchairs dumped on the curb – more trash destined for the landfill. Once on the tip, the chair may be broken, but the materials remain intact – a jumble of wooden frame, cotton covers, polyurethane cushions, thread, staples and glue.
A few months in, the thin thread and light glue that held the chair together would be all but gone. After half a year, the cotton that once covered the cushions, arms, and back will have rotted away. As the months turn into years, and the years into decades, the wooden frame will have slowly decomposed in the landfill – much slower than if it were in the elements.
After twenty years pass, the staples will have started to rust, with liquid finally working its way through the zinc coating to eat away at the iron. Decades turn into centuries and after half a millennium, the polyurethane cushions are no longer recognizable but still very much there.
A thousand years have passed since the armchair stood on the city curb and it is finally almost completely broken down.
That’s just one armchair, of the more than 12.2 million tons of American furniture waste in 2017 alone, 80.2% of which went to landfill.
Alternatives To Leaving Materials to Decompose
Dumping everything in a landfill for possibly millions of years is clearly not a sustainable model of waste management, especially when we see that the materials that take the longest to decompose are often easily recyclable:
Glass – left to break down, glass can take 1 million years. However, when dealt with responsibly, glass can be recycled endlessly with no loss in quality.
Plastic – while not endlessly recyclable, many plastics can be re-processed several times into new products before they start to break down. Even two uses are better than 500+ years in a landfill after a single use!
Aluminum – a can might take 100+ years to break down, but aluminum, like glass, can be recycled infinitely. It is one of the most easily recycled materials within our waste streams but still ends up degrading in landfills.
Paper – as with plastic, paper can only be reprocessed a limited number of times before it is no longer usable, but this is still better than sitting in a landfill for 5 months.
Materials that decompose quickly can also be better processed. Vegetable trimmings and fruit peels may break down in a matter of weeks or months, but this process is much better when they are separated out as Organics/Compost rather than tossed in a landfill.
Materials That Decompose Quickly, Slowly, or Not at All: Does It Matter?
When looking at the table above, it’s easy to justify tossing some trash in the knowledge that it will be “gone” in a matter of weeks or months. However, whether a material decomposes quickly, slowly, or not at all, adding it to landfill waste streams still has negative repercussions.
Even the most innocuous of waste – such as vegetable trimmings – can cause excessive methane production, water contamination, and more when left to decompose in the unnatural environment of a landfill.